Mobile network, such as GSM (Global System for Mobile communications) and UMTS (Universal Mobile Telecommunications System) and so on, adopting the circuit switched technique is called as Circuit Switched (CS) domain, which can provide basic voice services and supplementary services based on voice services for users.
In some parts of the world, such as Africa, South America and South Asia and so on, the lack of fast and reliable transmission resources or the presence of high transmission costs bring certain difficulties to the operators in implementing the deployment of network and service. However, the majority of calls in mobile network are local calls according to statistics in those places, which are generated in the same Base Station System (BSS). If a local switch technique (the voice data performing loop in BSS) is adopted in local calls, it can save the transmission resources of A port between a BSS and a core network MSC (Mobile Switch Center).
FIG. 1 is a schematic diagram of the traditional voice call, the User Equipment (UE) accesses BSS and MSC through CS domain. When UE1 calls UE2, UE1 sends a call setup request to the MSC to which the UE1 is accessed through the BSS; the MSC finds the called UE2 according to the location information of access of UE2 and informs the BSS to set up a radio bearer connected with the UE1 and UE2 and respectively sets up a bearer of the UE1 and UE2 between the BSS and MSC; and loop is performed on the bearer of both sides of MSC, which ensures a voice communication between the UE1 and UE2.
FIG. 2 is a schematic diagram of a voice call adopting the local call local switch technique, and compared with FIG. 1, the MSC judges whether the UE1 and UE2 belong to the same one BSS according to the cell when receiving a call setup request from the UE1, if the UE1 and UE2 belong to the same one BSS, the MSC informs the BSS to implement a local switch; the bearer loop of the UE1 and UE2 is implemented at the side of BSS, which can save the bearing resource between the BSS and MSC, that is the bearing resource of A port.
FIG. 3 is a signaling flow of the local call local switch technique adopted in FIG. 2, comprising following steps:
301, the UE1 and UE2 initiate calls under the same BSS, and set up a mutual connection through a core network MSC, and the MSC allocates a circuit number or a call identifier between the BSS and MSC to the calling UE1 and the called UE2;
302, the called UE2 responds in a ringing status, and sends a called response message to MSC through BSS;
303, the MSC sends the called response message to the calling UE1, and informs the UE1 that the call is connected;
304, the MSC judges whether the call is a local call belonging to the same one BSS according to the current location information of the calling UE1 and the called UE2;
305, if the call is a local call belonging to the same one BSS, the MSC sends a local switch command message to the BSS and informs the BSS to implement a local switch, and the local switch command message includes the circuit number or call identifier between the BSS and MSC which are allocated by the MSC to the calling UE1 and the called UE2 in the step 301;
306, the BSS receives the local switch command message, and associates the local switch command message with two ongoing communication conversations according to the circuit number or the call identifier of the calling and the called in the local switch command message, and performs loop on the voice data bearer thereof so as to implement the switch of voice bearer in the BSS;
307, the BSS sends a local switch success message to the MSC after the local switch succeeds; and
308, the MSC informs the BSS to release the voice bearer connection between the BSS and MSC after receiving the local switch success message, that is, release the bearer connection of the A port.
Regarding to the analysis of the above steps, if in a scenario of the BSS connecting with multiple MSCs shown in FIG. 4, the calling UE1 accesses the MSC1 through the BSS and the called UE2 accesses the MSC2 through the BSS, although the calling and the called initiate calls under the same BSS, the calling and the called are respectively accessed to different MSCs, which will lead to a problem that neither the MSC1 to which the calling UE1 is accessed nor the MSC2 to which the called UE2 is accessed can judge whether the call is a local call according to the location information of the calling and the called in the step 304, and ultimately lead to a problem that the local call can't implement a local switch.